The present invention is directed to integrated circuits and their processing for the manufacture of semiconductor devices. More particularly, the invention provides a method and apparatus for controlling etchback profile. Merely by way of example, the invention has been applied to making electrical connections between two metal levels. But it would be recognized that the invention has a much broader range of applicability.
Integrated circuits or “ICs” have evolved from a handful of interconnected devices fabricated on a single chip of silicon to millions of devices. Current ICs provide performance and complexity far beyond what was originally imagined. In order to achieve improvements in complexity and circuit density (i.e., the number of devices capable of being packed onto a given chip area), the size of the smallest device feature, also known as the device “geometry”, has become smaller with each generation of ICs. Semiconductor devices are now being fabricated with features less than a quarter of a micron across.
Increasing circuit density has not only improved the complexity and performance of ICs but has also provided lower cost parts to the consumer. An IC fabrication facility can cost hundreds of millions, or even billions, of dollars. Each fabrication facility will have a certain throughput of wafers, and each wafer will have a certain number of ICs on it. Therefore, by making the individual devices of an IC smaller, more devices may be fabricated on each wafer, thus increasing the output of the fabrication facility. Making devices smaller is very challenging, as each process used in IC fabrication has a limit. That is to say, a given process typically only works down to a certain feature size, and then either the process or the device layout needs to be changed. An example of such a limit is to make reliable electrical connections between two metal layers with low resistance.
Fabrication of custom integrated circuits using chip foundry services has evolved over the years. Fabless chip companies often design the custom integrated circuits. Such custom integrated circuits require a set of custom masks commonly called “reticles” to be manufactured. A chip foundry company called Semiconductor International Manufacturing Company (SMIC) of Shanghai, China is an example of a chip company that performs foundry services. Although fabless chip companies and foundry services have increased through the years, many limitations still exist. For example, electrical contacts between two metal layers usually have limited reliability and conductivity. These and other limitations are described throughout the present specification and more particularly below.
FIGS. 1 through 6 are simplified diagrams for a conventional method of making an electrical contact between two metal layers. These diagrams are merely examples, which should not unduly limit the scope of the claims herein. The method includes process 110 for via etching, process 120 for BARC etchback, process 130 for trench etching, process 140 for ashing, process 150 for stop layer removal, and process 160 for trench and via filling. At process 110 for via etching, via 112 is fabricated through silicon oxynitride layer 114 and FSG layer 116. FSG is usually composed of silicon oxide and fluorine. Silicon oxynitride layer 114 is located on FSG layer 116. Via 112 has via bottom 113 formed by a portion of silicon nitride layer 118. Another portion of silicon nitride layer 118 lies under FSG layer 116. Silicon nitride layer 118 is deposited on the surface of metal layer 119. At process 120 for BARC etchback, a BARC layer fills via 112 and is then etched back to form BARC layer 122. BARC stands for bottom anti-reflection coating. The BARC material is a conventional type of photoresist. At process 130 for trench etching, BARC layer 122 is further etched back to form BARC layer 132. Additionally, a portion of silicon oxynitride layer 114 and a portion of FSG layer 116 are removed to form trench 134. Trench 134 has trench bottom 136, a portion of which is composed of BARC and another portion of which is composed of FSG. At process 140 for ashing, BARC layer 132 is removed from via 112. At process 150 for stop layer removal, the part of silicon nitride layer 118 that forms via bottom 113 is removed. Consequently, metal layer 119 is exposed within via 112 and trench 134. At process 160 for trench and via filling, via 112 and trench 134 are filled with conductive material, such as copper, to form conductive filling layer 162. Conductive filling layer 162 forms an electrical contact between metal layer 119 and metal layer 164. Part of metal layer 164 lies on the surface of silicon oxynitride layer 114. The electrical contact usually has limited conductivity and reliability.
Hence, it is desirable to improve technique for making an electrical contact.